Communication systems that utilize coded communication signals are known in the art. One such system is a direct sequence code division multiple access (DS-CDMA) cellular communication system, such as set forth in the Telecommunications Industry Association Interim Standard 95A (TIA/EIA IS-95A) herein after referred to as IS-95A and incorporated herein by reference. In accordance with IS-95A, the coded communication signals used in the DS-CDMA system comprise signals that are transmitted in a common 1.25 MHz bandwidth to base sites of the system from communication units, such as mobile or portable radiotelephones, that are communicating in the coverage areas of the base sites. Each DS-CDMA signal includes, inter alia, a pseudorandom noise (PN) binary code associated with a particular base site and a PN sequence associated with a particular communication unit.
During a typical communication, a communication unit often travels within a coverage area of a base site that is supporting the communication. Such movement typically results in fading of the communication signal transmitted from the communication unit, henceforth referred to as a mobile unit, to the base site due to multipath propagation of the transmitted signal. As is known, multipath propagation results from the reflections of the transmitted signal off of nearby scatterers, such as buildings. These reflections produce replicas of the originally transmitted signal that arrive at the base site at various times depending on the effective propagation distances traveled by the replicas. The originally transmitted signal and multipath replicas are typically referred to as multipath signals of the originally transmitted signal.
To demodulate the transmissions from a particular mobile unit, a base site receiver must first identify the multipath signals associated with that mobile unit. This identification of a particular mobile unit's multipath signal(s), as well as their locations with reference to an offset in time (referred to as a pn-offset), is known in the art as an antenna, or signal, search.
In a sectorized antenna system, there are N sectors and M antennas for each of the sectors. For a typical demodulation process, the searching process is done within a single sector. The order of searching is typically set such that the antennas within a sector are searched serially. When multiple antennas are specified, the receiver may be directed to demodulate specific multipath signals only after all of the antennas have been searched. After all antennae have been searched, an interrupt, such as a sort.sub.-- done interrupt, may be generated and an array of eight data points, referred to as winning correlation energies, may be produced. It is these data points which are used to direct the receiver to demodulate specific multipath signals at specific pn-offset locations.
If a mobile unit is in a softer hand-off or sector-to-sector hand-off, N sectors may be involved, and a total of N.times.M antennas may be searched one after another during a complete searching process before the receiver begins the demodulation process. For example, if N=1, and M=2, then the normal traffic channel demodulation process has two antennas to be searched within one sector before a sort.sub.-- done interrupt is generated. In a two-way softer hand-off, the multipath demodulation process will have four antennas to be searched, two for each of the two sectors, prior to generating a sort.sub.-- done interrupt. Hence, receiver demodulation at the newly found signal path pn-offset, will typically not occur until sufficient time has elapsed to complete the serial search of all specified antennas.
Therefore, a need exists for a method for performing a signal search in a wireless communication system which significantly reduces the time interval from, receiving the communication signals at base site antennae, to demodulating the communication signals at the base site receiver.